Neptune's Small Moons Neptune's Small Moons orbit : 48,200 km from Neptune diameter : 58 km mass : ? The Naiads were the nymphs who lived in and presided over brooks, springs, and fountains. The last of the satellites discovered in 1989 by Voyager 2 . Naiad, Thalassa, Despina and Galatea are all irregularly shaped. More about Naiad orbit : 50,000 km from Neptune diameter : 80 km mass : ? Thalassa was a daughter of Aether and Hemera. "Thalassa" is also the Greek word for "sea". Discovered in 1989 by Voyager 2 . More about Thalassa orbit : 52,600 km from Neptune diameter : 148 km mass : ? Despina was a nymph, the daughter of Poseidon (Neptune) and Demeter. Discovered in 1989 by Voyager 2 . More about Despina orbit : 62,000 km from Neptune diameter : 158 km mass : ?

Galatea was a Sicilian Nereid loved by the Cyclops Polyphemus. (Not related to the maiden who was originally a statue carved by Pygmalion and who was brought to life by Aphrodite.) Discovered in 1989 by Voyager 2 . More about Galatea from LANL Open Issues We know next to nothing about these moons. Even the basic orbital and size data are not very accurate. Neptune's Small Moons Neptune's Small Moons orbit : 48,200 km from Neptune diameter : 58 km mass : ? The Naiads were the nymphs who lived in and presided over brooks, springs, and fountains. The last of the satellites discovered in 1989 by Voyager 2 . Naiad, Thalassa, Despina and Galatea are all irregularly shaped. More about Naiad Neptune's Small Moons Neptune's Small Moons orbit : 48,200 km from Neptune diameter : 58 km mass : ? The Naiads were the nymphs who lived in and presided over brooks, springs, and fountains.

The last of the satellites discovered in 1989 by Voyager 2 . Naiad, Thalassa, Despina and Galatea are all irregularly shaped. More about Naiad orbit : 50,000 km from Neptune diameter : 80 km mass : ? Thalassa was a daughter of Aether and Hemera. "Thalassa" is also the Greek word for "sea". Discovered in 1989 by Voyager 2 . More about Thalassa orbit : 52,600 km from Neptune diameter : 148 km mass : ? Despina was a nymph, the daughter of Poseidon (Neptune) and Demeter. Discovered in 1989 by Voyager 2 . More about Despina orbit : 62,000 km from Neptune diameter : 158 km mass : ? Galatea was a Sicilian Nereid loved by the Cyclops Polyphemus. (Not related to the maiden who was originally a statue carved by Pygmalion and who was brought to life by Aphrodite.) Discovered in 1989 by Voyager 2 .

More about Galatea from LANL Open Issues We know next to nothing about these moons. Even the basic orbital and size data are not very accurate. Home ... Neptune ... Naiad / Thalassa / Despina / Galatea ... Larissa ... Data Bill Arnett ; last updated: 2003 Nov 2 Neptune's Moons: 14 Discovered So Far Neptune's Moons: 14 Discovered So Far By Elizabeth Howell, Space.com Contributor | June 30, 2016 06:18pm ET MORE This diagram shows the orbits of several moons located close to the planet Neptune. All of them were discovered in 1989 by NASA's Voyager 2 spacecraft, with the exception of S/2004 N 1, which was discovered in archival Hubble Space Telescope images taken from 2004 to 2009. Image released July 15, 2013. Credit: NASA, ESA, and A. Feild (STScI) Neptune, the farthest planet from the sun, has 14 known moons.

Almost half of the discoveries took place decades after NASA's Voyager 2 spacecraft swung by the planet and its system, demonstrating just how far telescope technology has progressed. (One moon was also spotted in 2013 after being lost for nearly 25 years .) Moons of this planet are named for Greek or Roman mythological characters with links to Neptune, Poseidon, or the ocean, according to International Astronomical Union guidelines. The irregular satellites are named after the daughters of Nereus and Doris, who were attendants of Neptune. The latest moon discovery was announced in 2013. Scientists spotted the satellite — temporarily called called S/2004 N 1 — after analyzing old images from the Hubble Space Telescope . The moon is tiny, said to be about 100 million times fainter than what the naked eye can spot in the night sky . Early telescopic discoveries Due to Neptune's distance from Earth , only two moons were confirmed with ground telescopes before Voyager 2. The first one, Triton, was actually discovered only 17 days after the planet itself was found.

Triton is the only large moon in the solar system with a retrograde orbit, circling in the opposite direction of Neptune's rotation. Found by British astronomer William Lassell in 1846, it remained a small dot in a telescope for well over a century until the Voyager 2 spacecraft flew through Neptune's system in 1989. The moon, which is 1,680 miles (2,700 kilometers) in diameter, has few craters on it. The surface consists of "smooth volcanic plains, mounds and round pits formed by icy lava flows," according to NASA. Scientists believe Triton has a frozen nitrogen crust overlaying a rocky, metal core and ice-filled mantle. It also has a nitrogen atmosphere — likely created from volcanic activity — with methane traces. Voyager 2 also saw geysers, making Triton one of only a few moons known to be geologically active. Ahead of the New Horizons flyby of Pluto in 2015, NASA released the best-ever map of Triton because the two worlds were expected to be somewhat similar ; this would allow for comparisons.

Nereid is the other confirmed telescopic discovery, but it is much smaller: 105 miles (170 kilometers). It was discovered in 1949 by Dutch-American astronomer Gerard Kuiper, but was so small that Voyager 2 only managed to capture a distant, blurry image as it flew by. Scientists believe Nereid is a captured asteroid or Kuiper Belt Object because its orbit is eccentric, NASA stated. It is distant from Neptune, in an orbit that takes 360 Earth days to complete. Voyager 2's finds Voyager 2 flew through Neptune's system in August 1989, and found several satellites during its journey. Astronomers did technically spot Larissa , a 60-mile (97-kilometer) moon, in 1981 with a ground telescope. But it wasn't confirmed until 1989, when the spacecraft was close by. Voyager 2's images showed an asteroid-like body with a surface pockmarked with craters. The moon's orbit is slowly moving closer to Neptune. Scientists believe it will either smack into the planet's atmosphere, or break into a ring if tidal forces first rip the moon apart.

Proteus was a surprise find because it was so large: 130 miles (210 kilometers), bigger than the moon Nereid that was first spotted from Earth. Proteus, however, is much darker and could have eluded telescopic detection for that reason. The moon has a lumpy shape with many craters. If it was just a bit bigger, its gravity would pull the moon's shape closer to a sphere, NASA said. Tiny Naiad – which looks a bit like a potato in shape – probably is a combination of fragments from several Neptune satellites, NASA said. The moon wasn't found by astronomers again until 2013, when scientists used a different technique on Hubble Space Telescope images to reduce Neptune's glare – making the moon pop out. Thalassa probably has a similar composition to Naiad, but the planet is disc-shaped despite its small size. Both moons also have orbits that will eventually fall into Neptune. The spacecraft also found Galatea – which may have gravitational effects on Neptune's rings – and Despina , which is within the rings themselves.

Discoveries after Voyager 2 While there is no spacecraft en route to Neptune, telescope technology on the ground is improving with the aid of tools such as adaptive optics. There also are telescopes in space that don't have to fight through the Earth's atmosphere to see things. Both of these changes allowed many Neptune moon discoveries in the early 2000s. Four moon discoveries were announced at once in 2002: Laomedeia , Halimede , Sao and Neso . These moons are so small and distant that little is known about them besides their orbits. Most probably were formed after collisions from stray rocks in the vicinity. The team that found them used the 4-meter Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile, and the 3.6-meter Canada-France-Hawaii Telescope. Psamathe was found just a year later using the 8.3-meter Subaru reflector at the Mauna Kea Observatory. Neso's and Psamathe's orbits are somewhat similar, but not much more is known about the moon besides that. The last moon found to date has been discovered so recently that no official name is assigned to it.

Designated S/2004 N 1 for now, astronomers found the moon in 2013 through analyzing old Hubble Space Telescope images. It's just 12 miles (19 kilometers) in diameter. Further close-up observations of Neptune's moons will likely require another spacecraft, but as of mid-2016 none have been approved by NASA or the European Space Agency. Over the years, several working groups have proposed different ideas for getting to Neptune, but the mission concepts have yet to leave the drawing board due to reported budgetary or plutonium shortages (as plutonium is required to get a powered spacecraft out that far). As of 2015, however, NASA said it is considering looking at a Uranus or Neptune mission as a possible near-future “flagship” mission. Such a mission, however, likely wouldn't get to Neptune until the 2030s, or about 50 years after Voyager flew past. Credit: by Karl Tate, Infographics Artist Editor's Recommendations The moons of Neptune The moons of Neptune September 9, 2015 by Matt Williams, Universe Today Neptune and its moons.

Credit: NASA Neptune, that icy gas giant that is the eight planet from our Sun, was discovered in 1846 by two astronomers – Urbain Le Verrier and Johann Galle. In keeping with the convention of planetary nomenclature, Neptune was named after the Roman god of the sea (the equivalent to the Greek Poseidon). And just seventeen days after it was discovered, astronomers began to notice that it too had a system of moons. Initially, only Triton – Neptune's largest moon – could be observed. But by the mid-20th century and after, thanks to improvements in ground-based telescopes and the development of robotic space probes, many more moons would be discovered. Neptune now has 14 recognized satellites, and in honor of of their parent planet, all are named for minor water deities in Greek mythology. Discovery and Naming: Triton, being the largest and most massive of Neptune's moons, was the first to be discovered. It was observed by William Lassell on October 10th, 1846, just seventeen days after Neptune was discovered. It would be almost a century before any other moons would be discovered.

The first was Nereid, Neptune's second largest and most massive moon, which was discovered on May 1st, 1949, by Gerard P. Kuiper (for whom the Kuiper Belt is named) using photographic plates from the McDonald Observatory in Fort Davis, Texas. The third moon, later named Larissa, was first observed by Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky and David J. Tholen on May 24th, 1981. The discovery of this moon was purely fortuitous, and occurred as a result of the ongoing search for rings similar to those discovered around Uranus four years earlier. If rings were in fact present, the star's luminosity would decrease slightly just before the planet's closest approach. While observing a star's close approach to Neptune, the star's luminosity dipped, but only for several seconds. This indicated the presence of a moon rather than a ring. No further moons were found until Voyager 2 flew by Neptune in 1989.

In the course of passing through the system, the space probe rediscovered Larissa and discovered five additional inner moons: Naiad, Thalassa, Despina, Galatea and Proteus. In 2001, two surveys using large ground-based telescopes – the Cerro Tololo Inter-American Observatory and the Canada-France-Hawaii telescopes – found five additional outer moons bringing the total to thirteen. Follow-up surveys by two teams in 2002 and 2003 respectively re-observed all five of these moons – which were Halimede, Sao, Psamathe, Laomedeia, and Neso. And then on July 15th, 2013, a team of astronomers led by Mark R. Showalter of the SETI Institute revealed that they had discovered a previously unknown fourteenth moon in images taken by the Hubble Space Telescope from 2004–2009. The as yet unnamed fourteenth moon, currently identified as S/2004 N 1, is thought to measure no more than 16–20 km in diameter. In keeping with astronomical convention, Neptune's moons are all taken from Greek and Roman mythology.

In this case, all are named for gods of the sea, or for the children of Poseidon (which include Triton, Proteus, Depsina and Thalassa), minor Greek water dieties (Naiad and Nereid) or Nereids , the water nymphs in Greek mythology (Halimede, Galatea, Neso, Sao, Laomedeia and Psamathe). However, many of the moons were not officially named until the 20th century. The name Triton, which was originally suggested by Camille Flammarion in his 1880 book Astronomie Populaire , but not into common usage until at least the 1930s. Inner (Regular) Moons: Neptune's Regular Moons are those located closest to the planet and which follow circular prograde orbits that lie in the planet's equatorial plane.

They are, in order of distance from Neptune: Naiad (48,227 km), Thalassa (50,074 km), Despina (52,526 km), Galatea (61,953 km), Larissa (73,548 km), S/2004 N 1 (105,300 ± 50 km), and Proteus (117,646 km). All but the outer two are within Neptune-synchronous orbit (meaning that orbit Neptune slower than it's orbital period (0.6713 days) and thus are being tidally decelerated. The inner moons are closely associated with Neptune's narrow ring system. The two innermost satellites, Naiad and Thalassa, orbit between the Galle and LeVerrier rings, whereas Despina orbits just inside the LeVerrier ring. The next moon, Galatea, orbits just inside the most prominent Adams ring and its gravity helps maintaining the ring by containing its particles. Hubble Space Telescope composite picture showing the location of a newly discovered moon, designated S/2004 N 1.

Credit: NASA, ESA, and M. Showalter (SETI Institute). Based on observational data and assumed densities, Naiad measures 96 × 60 × 52 km and weighs approximately 1.9 x 1017 kg. Meanwhile, Thalassa measures 108 x 100 × 52 km and weighs 3.5 x 1017 kg; Despina measures 180 x 148 x 128 and weighs 21 x 1017 kg; Galatea measures 204 x 184 x 144 and weighs 37.5 x 1017 kg; Larissa measures 216 x 204 x 168 and weighs 49.5 x 1017 kg; S/2004 N1 measures 16-20 km in diameter and weighs 0.5 ± 0.4 x 1017 kg; and Proteus measures 436 x 416 x 402 and weighs 50.35 x 1017 kg.

Only the two largest regular moons have been imaged with a resolution sufficient to discern their shapes and surface features. Nevertheless, with the exception of Larissa and Proteus (which are largely rounded) all of Neptune's inner moons are believed to be elongated in shape. In addition, all the inner moons dark objects, with geometric albedo ranging from 7 to 10%. Their spectra also indicated that they are made from water ice contaminated by some very dark material, probably organic compounds. In this respect, the inner Neptunian moons are similar to the inner moons of Uranus. Outer (Irregular) Moons: Neptune's irregular moons consist of the planet's remaining satellites (including Triton). They generally follow inclined eccentric and often retrograde orbits far from Neptune; the only exception is Triton, which orbits close to the planet following a circular orbit, though retrograde and inclined. In order of their distance from the planet, the irregular moons are Triton, Nereid, Halimede, Sao, Laomedeia, Neso and Psamathe, a group that includes both prograde and retrograde objects.

With the exception of Triton and Nereid, Neptune's irregular moons are similar to those of other giant planets and are believed to have been gravitationally captured by Neptune. In terms of size and mass, the irregular moons are relatively consistent, ranging from approximately 40 km in diameter and 4 x 1016 kg in mass (Psamathe) to 62 km and 16 x 1016 kg for Halimede. Triton and Nereid: Triton and Nereid are unusual irregular satellites and are thus treated separately from the other five irregular Neptunian moons. Between these two and the other irregular moons, four major differences have been noted. First of all, they are the largest two known irregular moons in the Solar System. Triton itself is almost an order of magnitude larger than all other known irregular moons and comprises more than 99.5% of all the mass known to orbit Neptune (including the planet's rings and thirteen other known moons). Secondly, they both have atypically small semi-major axes, with Triton's being over an order of magnitude smaller than those of all other known irregular moons.

Thirdly, they both have unusual orbital eccentricities: Nereid has one of the most eccentric orbits of any known irregular satellite, and Triton's orbit is a nearly perfect circle. Finally, Nereid also has the lowest inclination of any known irregular satellite With a mean diameter of around 2700 km and a mass of 214080 ± 520 x 1017 kg, Triton is the largest of Neptune's moons, and the only one large enough to achieve hydrostatic equilibrium (i.e. is spherical in shape). At a distance of 354,759 km from Neptune, it also sits between the planet's inner and outer moons. The video will load shortly Triton follows a retrograde and quasi-circular orbit, and is composed largely of nitrogen, methane, carbon dioxide and water ices. With a geometric albedo of more than 70% and a Bond albedo as high as 90%, it is also one of the brightest objects in the Solar System. The surface has a reddish tint, owning to the interaction of ultraviolet radiation and methane, causing tholins.

Triton is also one of the coldest moons in the Solar System, with surface temperature of about 38 K (235.2 °C). However, owing to the moon being geologically active (which results in cryovolcanism) and surface temperature variations that cause sublimation, Triton is one of only two moons in the Solar System that has a substantial atmosphere. Much like it's surface, this atmosphere is composed primarily of nitrogen with small amounts of methane and carbon monoxide, and with an estimated pressure of about 14 ?bar. Triton has a relatively high density of about 2 g/cm3 indicating that rocks constitute about two thirds of its mass, and ices (mainly water ice) the remaining one third. There also may be a layer of liquid water deep inside Triton, forming a subterranean ocean. Surface features include the large southern polar cap, older cratered planes cross-cut by graben and scarps, as well as youthful features caused by endogenic resurfacing. Because of its retrograde orbit and relative proximity to Neptune (closer than the Moon is to Earth), Triton is grouped with the planet's irregular moons (see below).

In addition, it is believed to be a captured object, possibly a dwarf planet that was once part of the Kuiper Belt. At the same time, these orbital characteristics are the reason why Triton experiences tidal deceleration. and will eventually spiral inward and collide with the planet in about 3.6 billion years. Nereid is the third-largest moon of Neptune. It has a prograde but very eccentric orbit and is believed to be a former regular satellite that was scattered to its current orbit through gravitational interactions during Triton's capture. Water ice has been spectroscopically detected on its surface. Nereid shows large, irregular variations in its visible magnitude, which are probably caused by forced precession or chaotic rotation combined with an elongated shape and bright or dark spots on the surface. The video will load shortly Formation: Given the lopsided distribution of mass in its moons, it is widely believed that Triton was captured after the formation of Neptune's original satellite system – much of which would have been destroyed in the process of capture. Many theories have been offered regarding the mechanisms of its capture over the years.

The video will load shortly The most widely-accepted is that Triton is a surviving member of a binary Kuiper Belt Object that was disrupted with an encounter with Neptune. In this scenario, Triton's captured was the result of a three-body encounter, where it fell into a retrograde orbit while the other object was either destroyed or ejected in the process. Triton's orbit upon capture would have been highly eccentric, and would have caused chaotic perturbations in the orbits of the original inner Neptunian satellites, causing them to collide and reduce to a disc of rubble. Only after Triton's orbit became circular again could some of the rubble re-accrete into the present-day regular moons. This means it is likely that Neptune's present inner satellites are not the original bodies that formed with Neptune. Global Color Mosaic of Triton, taken by Voyager 2 in 1989. Credit: NASA/JPL/USGS Numerical simulations show that there is a 0.41 probability that the moon Halimede collided with Nereid at some time in the past.

Although it is not known whether any collision has taken place, both moons appear to have similar ("grey") colors, implying that Halimede could be a fragment of Nereid. Given its distance from the Sun, the only mission to ever study Neptune and its moons up close was the Voyager 2 mission. And though no missions are currently being planned, several proposals have been made that would see a robotic probe dispatched to the system sometime in the late 2020s or early 2030s. Using the CRIRES instrument on ESO’s Very Large Telescope, a team of astronomers has been able to see that the summer is in full swing in Triton’s southern hemisphere. Credit: ESO Neptune - its history Neptune - its history red shift and big bang problems with Big Bang of the name Cosmic Elk or cosmicelk Neptune and its strange moons The orbit of Uranus was calculated using Kepler's and Newton's laws. The calculations took several years. At that time computers were people who did the calculations and they had to be paid. French astronomer Alexis Bouvard undertook the task.

He used both the modern observations from 1781, and also the early observations of Flamsteed in 1690, Bradley, Mayer in 1756, and Le Monnier. At least 22 observations of Uranus had been made from 1690 to 1772 but it had not been recognised as a planet. Bouvard found that he could not obtain an orbit which would fit all the sets of observations during that 130 years that he was able to obtain his data. There were two possibilities. One was that the earlier observational data was unreliable - some of Pierre Charles Le Monnier's records had been made on a paper bag that had contained his wig powder. The other possibility, was, since allowance had already been made for the influence of Jupiter and Saturn, that there must be another large planet beyond Uranus affecting its orbit and waiting to be discovered. If so, where was it. In 1841 a young Cambridge mathematics student, John Couch Adams, resolved to calculate the position of the unknown planet, but he did not have the time to apply himself to the task until 1843.

By September 1845, he had a result that indicated the place in the sky where the missing planet could be found. He took his results to the Astronomer Royal George Biddel Airy, who had been his professor at Cambridge. Airy did not trouble himself to come to the door, but sent a message that he was at supper and could not be disturbed. Adams left his paper with the servant who put it away in Airy's study. Meanwhile in Paris, the astronomer, Urbain Jean Joseph Le Verrier was working on the same problem, unaware of Adams' paper since it had been ignored by Airy. At the end of 1845 he presented his paper. Airy received a copy in England and it stimulated him to search his shelves for Adams's paper. The two papers were very close in pinpointing the position of the unknown planet. The Director of the Cambridge Observatory, James Challis, was requested to search for the planet, but could not find any charts for that region of the sky.

Meanwhile, Le Verrier had revised and updated his paper and in September 1846, sent a copy to Encke at Berlin together with a letter asking if he could help in searching for it. Encke asked two of his assistants, Heinrich D'Arrest and Johann Galle to do this. They already had a recently compiled map of that part of the sky. Galle called out the visible stars one by one while D'Arrest checked them on the map. Suddenly they come upon an unmarked object which at the moment looked like an 8th magnitude star. The next night they found it again, and subsequent checking showed it to be moving against the background of stars - they had found the missing planet! Adams had only been 2 1/2" out and Le Verrier even closer at less that 1" out in the position of Neptune. The discovery of the new planet was of great interest all over the world, but England, France and Germany squabbled over the claim to have been the first to have discovered it. Neptune is about 4,500 million miles from the Sun and its orbit takes 165 Earth years.

Although it receives only about 1/900th as much sunlight as Earth, this is sufficent to significantly affect the planet's atmosphere with temperature variations consistent with seasonal changes. At present it is summer at Neptune's south pole which has been tilted towards the Sun for about 40 years. It has been discovered that the temperature there is about 10 degrees higher than the average temperature over the rest of Neptune which is minus 200 degrees Celsius. It is the warmer polar area that allows methane gas to seep out of the lower atmosphere to the surface. Voyager 2 arrived here at the end of August 1989. Two moons were known, Triton and Nereid, six more were discovered and rings round Neptune and a strong magnetic field at an angle of 47 degrees to its axis. It took four hours for the information from Voyager 2 to reach Earth. Neptune like the other gas giants, is mostly composed of the light gases, hydrogen and helium. But the abundance of methane in Neptune's upper atmosphere absorbs the red light from the Sun and reflects the blue light back into space, making Neptune, like Uranus, appear blue. Neptune has the fiercest winds in the solar system.

The winds blow at speeds up to 300 m.p.h. from east to west which is the opposite directions to the winds on the other gas giants. In the bands of clouds Voyager 2 showed a is a great dark whirling storm spot, rather like the great red spot on Jupiter and smaller storm whirls. There are also bright white clouds at a very high altitude. In 1994 the Hubble Space telescope showed that the storm spots seen by Voyager 2 in 1989, had changed, and had been replaced with different cloud formations. Like Jupiter, Neptune has an internal heat source. Like the other gas giants, it is really a small star, too small for gravitation pressures to heat its core sufficiently for nuclear fusion to take place. Neptune's Moons Triton Neptune's largest moon, discovered by Lassell in 1846, is 1350 ± 5 kilometres in radius with a density of 2.075 ± 0.019. Its orbit is retrograde which means that it travels in the opposite direction to most of the bodies in the solar system. Its orbit round Neptune is irregular in other ways.

Normally a planet's satellites orbit parallel to its equator, but the orbit of Triton is at an angle of 21 degrees to Neptune's equator. This means that Triton is unlikely to have formed from a disc of material round Neptune, so it must have been an independent planet, a Kuiper object, much like Pluto, dragged into orbit round Neptune. Triton is pink and blue and it is geologically active with volcanos venting dust and gas. Part of the terrain has a young surface flooded with ice lava. Part of the surface is crisscrossed with faults, possibly grabens, that is sunken faults. The surface temperature of Triton is very low - about 38K (water freezes at 273.15K, which is 0 degrees C). Triton is very bright - average albedo is 0.78. This is because the surface is covered by a pink methane and nitrogen frost. It has a polar cap of nitrogen ice which is probably seasonal.

Triton has a thin nitrogen atmosphere, pressure 16 ± 3 m bar - a hundred thousandth of Earth's atmospheric pressure, but enough for thin clouds of nitrogen ice over the polar cap at a height of a few kilometres. The surface features on Triton are named after aquatic gods and places. Nereid was discovered in 1949 by Gerard Kuiper. Nereid is about 340 kilometres in diameter and is so far from Neptune that it requires 360 days to make one orbit. Nereid's orbit is the most eccentric in the solar system. Its distance to Neptune ranges from about 1,353,600 kilometres (841,100 miles) to 9,623,700 kilometres. The satellites discovered by Voyager 2 in 1989, are all very dark objects. Naiad discovered by Voyager 2 in 1989, is about 54 kilometres in diameter and orbits Neptune every 7 hours and 6 minutes about 23,200 kilometres above the clouds. It is irregularly shaped.

Naiad circles the planet in the same direction as Neptune rotates, and remains close to Neptune's equatorial plane. Thalassa discovered by Voyager 2 in 1989, is about 80 kilometres in diameter. It orbits Neptune in 7 hours, 30 minutes about 25,200 kilometres above the cloud tops. It is irregularly shaped. Thalassa circles the planet in the same direction as Neptune rotates. Despina discovered by Voyager 2 in 1989, is only 27,700 kilometres from Neptune's clouds, orbits every 8 hours. Its diameter is about 150 kilometres. It is irregularly shaped. Despina circles the planet in the same direction as Neptune rotates, and remains close to Neptune's equatorial plane. Galatea discovered by Voyager 2 in 1989, is 37,200 kilometres from Neptune. It has a diameter of 180 kilometres and completes an orbit in 10 hours, 18 minutes. It is irregularly shaped, circles the planet in the same direction as Neptune rotates, and remains close to Neptune's equatorial plane.

Larissa discovered by Voyager 2 in 1989, is about 48,800 kilometres from Neptune's clouds, and circles the planet in 13 hours, 18 minutes. Its diameter is about 190 kilometres. It is irregularly shaped, circles the planet in the same direction as Neptune rotates, and remains close to Neptune's equatorial plane. Proteus discovered by Voyager 2 in 1989, reflects only 6 percent of the sunlight that strikes it. Proteus is about 400 kilometres in diameter. Proteus orbits Neptune at a distance of about 92,800 kilometres above the cloud tops, and completes one orbit in 26 hours, 54 minutes. Proteus is irregularly shaped, circles the planet in the same direction as Neptune rotates, and remains close to Neptune's equatorial plane. In 2004, five more satellites - and one possible moon - have been discovered orbiting Neptune, bringing its tally of moons to 13. Two orbit in the same direction as the planet rotates, while the orbits of the others are opposite to Neptune's spin. The tiny outer satellites are probably captured asteroids.

Cataclysmic events connected to the capture of Neptune's moon Triton were thought to have destroyed any outer satellites the planet once had. The new moons, named S/2002 N1 to N4 and S/2003 N1, are in eccentric, tilted orbits. They are all between 30km and 50km in diameter. An international team of astronomers searched for the satellites between 2001 and 2003 using the 4m Cerro Tololo Inter-American Observatory and the 3.6m Canada-France-Hawaii telescope. The researchers used a technique to look for the new moons that was originally developed to detect very faint objects in the outer Kuiper Belt. They also observed a sixth candidate moon, which they have named c02N4. This was discovered on 14 August 2002 and seen again at the Very Large Telescope (VLT) on 3 September 2002. But further attempts to spot this object failed. The researchers say this could be Centaur - an object that has migrated from the outer Kuiper Belt. But its lack of movement relative to Neptune is more consistent with it being a satellite.

The satellites are unlikely to have condensed from material around Neptune. Instead, these so-called irregular moons may be the product of a parent body that collided with Neptune's moon Nereid and were then disturbed in their orbits by the capture of Triton from the Kuiper Belt. more on Neptune: Moons Moons: Moons are `fossils" into a planet's past.

The major, named moon systems are: Earth: Luna (The Moon) Mars: Deimos, Phobos Jupiter: Adrastea, Amalthea, Ananke, Callisto, Carme, Elara, Europa, Ganymede, Himalia, Io, Leda, Lysithea, Metis, Pasiphae, Sinope, Thebe Saturn: Atlas, Calypso, Dione, Enceladus, Epimetheus, Helene, Hyperion, Iapetus, Janus, Mimas, Pan, Pandora, Phoebe, Prometheus, Rhea, Telesto, Tethys, Titan Uranus: Ariel, Belinda, Bianca, Cordelia, Cressida, Desdemona, Juliet, Miranda, Oberon, Ophelia, Portia, Puck, Rosalind, Titania, Umbriel Neptune: Despina, Galatea, Larissa, Naiad, Nereid, Proteus, Thalassa, Triton Pluto: Charon (note: Pluto/Charon form a binary system, but Charon is the smaller so it is classed as the moon of Pluto) New, smaller moons are being discovered all the

 time with recent space missions.

The total count of moons (as of 12/18/2001) are: Mercury - 0 moons Mars - 2 moons Uranus - 20 moons Venus - 0 moons Jupiter - 28 moons Neptune - 8 moons Earth - 1 moon Saturn - 30 moons Pluto - 1 moon Moons range in shape from highly irregular to spheres. Their shape reflects their formation history, irregular objects are ill-formed moons (captured asteroids or comets) or pieces of a larger moon, spherical objects were once molten spheres, probably at the time of their formation. Moons of Mars: Deimos & Phobos We speculate, from their irregular appearances and low mean densities, that Deimos and Phobos, are captured asteroids. Both Deimos and Phobos are saturated with craters. Deimos has a smoother appearance caused by partial filling of some of its craters. Moons of Jupiter: Jupiter has 63 confirmed moons as of Jan 2009, i.e. moons with known orbits around Jupiter. Eight of these moons are regular, meaning they have prograde, nearly circular orbits.

They are composed of the four Galilean satellites, plus the inner or Amalthea group: Adrastea is a typical small moon Metis is the innermost known satellite of Jupiter Amalthea is one of Jupiter's smaller, irregular moons, an example of moon collecting dust from another moon (Io) The remaining 55 moons are irregular, they have a mixture of prograde and retrograde orbits with high inclinations and eccentricities. Jupiter's regular satellites are believed to have formed from a circumplanetary disk, a ring of accreting gas and solid debris analogous to a protoplanetary disk. The irregular satellites are substantially smaller objects with more distant and eccentric orbits. They form families with shared similarities in orbit (semi-major axis, inclination, eccentricity) and composition; it is believed that these are at least partially collisional families that were created when larger (but still small) parent bodies were shattered by impacts from asteroids captured by Jupiter's gravitational field. Moons of Saturn: The moons of Saturn are numerous and diverse, ranging from tiny moonlets less than 1 kilometer across to the enormous Titan, which is larger than the planet Mercury.

Saturn has sixty-two moons with confirmed orbits, fifty-three of which have names, and only thirteen of which have diameters larger than 50 kilometers. Saturn has seven moons that are large enough to become spherical. Twenty-four of Saturn's moons are regular satellites; they have prograde orbits not greatly inclined to the Saturn's equatorial plane. These include the seven major satellites, four small moons which exist in a Trojan orbit with larger moons, two mutually co-orbital moons and two moons which act as shepherds of Saturn's F Ring. Two other known regular satellites orbit within gaps in Saturn's rings. The relatively large Hyperion is locked in a resonance with Titan. The remaining regular moons orbit near the outer edge of the A Ring, within G Ring and between the major moons Mimas and Enceladus. The regular satellites are traditionally named after Titans and Titanesses or other figures associated with the mythological Saturn. The remaining thirty-eight, all small except one, are irregular satellites, whose orbits are much farther from Saturn, have high inclinations, and are mixed between prograde and retrograde. These moons are probably captured minor planets, or debris from the breakup of such bodies after they were captured, creating collisional families.

The irregular satellites have been classified by their orbital characteristics into the Inuit, Norse, and Gallic groups, and their names are chosen from the corresponding mythologies. The largest of the irregular moons is Phoebe, the ninth moon of Saturn, discovered at the end of the 19th century. The rings of Saturn are made up of objects ranging in size from microscopic to hundreds of meters, each of which is on its own orbit about the planet. Thus, a precise number of Saturnian moons cannot be given, as there is no objective boundary between the countless small anonymous objects that form Saturn's ring system and the larger objects that have been named as moons. At least 150 moonlets embedded in the rings have been detected by the disturbance they create in the surrounding ring material, though this is thought to be only a small sample of the total population of such objects. Daphnis drifts through the Keeler gap Atlas the second of Saturn's known satellites, orbits near the outer edge of the A-ring Enceladus is one of the innermost moons of Saturn.

Enceladus reflects almost 100 percent of the sunlight that strikes it and has evidence of internal heating and recent resurfacing effects Hyperion is one of the smaller moons of Saturn. It has a pock-marked body and is the largest irregularly shaped satellite ever observed.

Iapetus is one of the stranger moons of Saturn, its leading side is dark with a slight reddish color while its trailing side is bright Dione is the densest moon of Saturn other than Titan, and has several usual characteristics: 1) has a rocky core and ice crust, 2) is heavy cratering on trailing hemisphere, 3) has bright, wispy features Rhea is the largest airless satellite of Saturn that has different regions with different crater sizes indicating that parts of the moon have undergone resurfacing since formation Mimas is one of the innermost moons of Saturn with a very large impact crater that came close to fracturing the moon Tethys is an icy body similar in nature to Dione and Rhea Phoebe is the last of the known satellites of Saturn and orbits in a retrograde direction (opposite to the direction of the other satellites' orbits) in a plane much closer to the ecliptic than to Saturn's equatorial plane. Thus, Phoebe may be a captured asteroid with a composition unmodified since the time it was formed in the outer Solar System.

Moons of Uranus: Uranus, the seventh planet of the Solar System, has 27 known moons, all of which are named after characters from the works of William Shakespeare and Alexander Pope. William Herschel discovered the first two moons, Titania and Oberon, in 1787, and the other spherical moons were discovered in 1851 by William Lassell (Ariel and Umbriel) and in 1948 by Gerard Kuiper (Miranda). The remaining moons were discovered after 1985, either during the Voyager 2 flyby mission or with the aid of advanced Earth-based telescopes. A montage of Uranus' large moons and one smaller moon: from left to right Puck, Miranda, Ariel, Umbriel, Titania and Oberon. Uranian moons are divided into three groups: thirteen inner moons, five major moons, and nine irregular moons. The inner moons are small dark bodies that share common properties and origins with the planet's rings. The five major moons are massive enough to have achieved hydrostatic equilibrium (they were once molten spheres), and four of them show signs of internally driven processes such as canyon formation and volcanism on their surfaces.

The largest of these five, Titania, is 1,578 km in diameter and the eighth-largest moon in the Solar System, and about 20 times less massive than Earth's Moon. Uranus's irregular moons have elliptical and strongly inclined (mostly retrograde) orbits at great distances from the planet. Ariel is a relatively small satellite and is the brightest moon of Uranus Miranda with a jumbled surface unlike anything in the Solar System, indicates evidence of violent past with possible multiple shattering and reassembly Titania is the largest moon of Uranus and is marked by a few large impact basins Moons of Neptune: Neptune has thirteen known moons, by far the largest of which is Triton, discovered by William Lassell just 17 days after the discovery of Neptune itself. Over a century passed before the discovery of the second natural satellite, called Nereid. Neptune's moons are named for minor water deities in Greek mythology. Unique among all large planetary moons, Triton is an irregular satellite, as its orbit is retrograde to Neptune's rotation and inclined relative to the planet's equator.

The next-largest irregular satellite in the Solar System, Saturn's moon Phoebe, is only 0.03% Triton's mass. Triton is massive enough to have achieved hydrostatic equilibrium and to retain a thin atmosphere capable of forming clouds and hazes. Both its atmosphere and its surface are composed mainly of nitrogen with small amounts of methane and carbon monoxide. Triton's surface appears relatively young, and was probably modified by internally driven processes within the last few million years. The temperature at its surface is about 38K. Inward of Triton are six regular satellites, all of which have prograde orbits in planes that lie close to Neptune's equatorial plane. Some of these orbit among Neptune's rings. The largest of them is Proteus. Neptune also has six outer irregular satellites, including Nereid, whose orbits are much farther from Neptune, have high inclinations, and are mixed between prograde and retrograde. The two outermost ones, Psamathe and Neso, have the largest orbits of any natural satellites discovered in the Solar System to date. Proteus is one of the darkest objects in the Solar System

Question: Despina and Thalassa are two satellites of which planet?
Answer: Neptune